Gripping apparatus

ABSTRACT

Gripping apparatus comprises a plurality of axially tapered rollers ( 47 ) for engaging the gripped member; and a body having a cam surface ( 36 ) which is shaped so as to urge the rollers, when in use, against the gripped member when the rollers slide axially with respect to the cam surface. The cam surface is also shaped so as to urge the rollers, when in use, against the gripped member when the rollers roll along the cam surface.

The present invention relates to gripping apparatus.

A conventional gripping apparatus is shown in FIG. 16, and described indetail in WO 01/21933. Jaws 90, 91 are pivotable about rods 92,93. Jaw90 carries a semi-circular cage 94 containing rollers 95. Jaw 91 carriesa semi-circular cage 96 containing rollers 97. The inner faces of thejaws 90,91 have recesses which receive the rollers 95,97.

When it is desired to grip tubular 98, The cages 94,96 are rotatedrelative to the jaws 90,91. This causes the rollers to roll along theirrespective recesses and become wedged between the tubular and the jaw.

A first aspect of the invention provides gripping apparatus comprising aplurality of rollers which taper axially from a relatively narrow end toa relatively wide end; and a body having a cam surface which is shapedso as to urge the rollers against a gripped member, when in use, whenthe rollers translate axially with respect to the cam surface, and whichis also shaped so as to urge the rollers against the gripped member whenthe rollers roll along the cam surface.

The use of tapered rollers provides a number of advantages compared tothe parallel-sides rollers described in WO 01/21933. Firstly, therollers can provide resistance to both axial and rotational forces.Secondly, the system is more flexible because the rollers can be engagedin two different ways (that is, by sliding axially or by rolling).Thirdly, the apparatus can accommodate different gripped members with awider variety of sizes. Fourthly, the rollers can be more densely packedbecause a smaller amount of rolling movement needs to be accommodated.Fifthly, axial engagement of the rollers can be achieved more easilyusing a linear drive device such as a hydraulic or pneumatic cylinder.

Preferably the apparatus further comprises an actuator for generatingrelative axial and/or rolling movement between the rollers and the camsurface to urge the rollers against the gripped member.

The actuator may engage the rollers and/or the cam surface. The camsurface or the rollers may remain stationary during the relativemovement.

In a preferred embodiment, the rollers are moved by a cage coupled to ahand operated lever. Alternatively, the actuator may include a hydraulicor pneumatic cylinder.

Preferably the actuator comprises a plurality of resilient members, suchas leaf springs, each coupled with a respective roller. The resilientmembers can then flex by different amounts if one of the rollers becomesstuck.

The angle of taper of the rollers may vary, but preferably isapproximately constant along the length of the rollers.

The rollers may have a non-circular (e.g. elliptical) cross-section buttypically are substantially circular in cross-section.

Most preferably the rollers are substantially frustoconical.

In one embodiment all of the rollers taper in the same direction. Inanother embodiment the direction of taper of the rollers alternatesbetween successive rollers. This ‘top-and-tail’ arrangement permits therollers to be packed more densely.

Typically the cam surface is formed with a plurality of recesses, eachrecess receiving a respective roller.

The body may comprise a single fixed piece, or may comprise two or morejaws which can be opened to admit the gripped member.

A second aspect of the invention provides apparatus for gripping adownhole tubular comprising gripping apparatus according to the firstaspect of the invention.

The apparatus is particularly suited to such uses, in which the downholetubular may be pipe casing, a drill string, or any other tubularassociated with subterranean operations, typically in the oilfieldindustry.

For instance the apparatus may be of use in a power tong for grippingand rotating the downhole tubular, a backup for gripping and securingthe downhole tubular against rotational movement, or in an elevator forsecuring the downhole tubular against axial and rotational movement.

A third aspect of the invention provides a socket wrench comprisinggripping apparatus according to the first aspect of the invention. Thisprovides an alternative application for the apparatus. In this case, thegripped member is an integral part of the apparatus, and comprises oneor more sockets, typically hexagonal shaped.

A conventional method of gripping a downhole tubular is described inU.S. Pat. No. 5,845,549 and U.S. Pat. No. 4,084,453. Gripping memberswith sharp teeth are forced into engagement with the tubular. A problemwith this method is that the teeth cause permanent deformation of thetubular. In certain circumstances this can present serious problems. Forinstance, in a sour gas well, corrosive gases such as Hydrogen Sulphideand Carbon Dioxide will be present. If the tubular is formed with amaterial such as Chromium, these gases will corrode the tubular morequickly if the tubular has a rough deformed surface.

A fourth aspect of the invention provides a method of handling adownhole tubular comprising gripping the tubular with a plurality ofgripping members arranged circumferentially around the pipe; andtransferring rotational and/or longitudinal forces to or from thetubular, wherein the tubular is gripped in such a manner so as not toexceed the elastic deformation limit of the tubular while the forces arebeing transferred.

The advantage of the fourth aspect of the invention is that itsubstantially avoids permanent deformation of the tubular.

Typically the method comprises urging the gripping members against thetubular by a wedging action. This wedging action tends to spread thegripping force over a relatively wide area, thus avoiding excessivedeformation of the tubular.

Typically the gripping member comprises a roller. The roller may have awide variety of shapes including cylindrical, frustoconical, sphericalor asymmetric—for instance the ‘dog bone’ shape shown in FIG. 13 ofWO01/21933.

The gripping method may be employed during a variety of downholeoperations. For example the tubular may be gripped while it is coupled(for instance by screwing) with an additional length of downholetubular.

Typically the maximum deformation of the tubular is greater than 10% andless than 100% of the elastic limit.

A number of embodiments of the invention will now be described by way ofexample only and with reference to the accompanying drawings, in which:

FIG. 1 is a sectional side view of a pipe string gripping mechanism;

FIG. 2 is a cross-section taken along line A-A in FIG. 1;

FIG. 3 is a side view of the mechanism from the right-hand side of FIG.1 with the actuator handle in a partially raised position;

FIG. 4 a is a view of the cage as viewed from inside the bore of themechanism, with no pipe casing present;

FIG. 4 b is a view of an alternative cage;

FIG. 4 c is a view of a further alternative cage;

FIG. 5 is a plan view of an oil field tong incorporating the mechanismof FIGS. 1-4;

FIG. 5 a is a plan view of an adapter plate;

FIG. 6 shows the tong with the gripping jaws open;

FIG. 7 is a sectional view of an alternative pipe string grippingmechanism with inverted rollers;

FIG. 8 is a perspective view of an alternative pipe string grippingmechanism with alternating rollers;

FIG. 9 a is a view of the cage as viewed from inside the bore of themechanism of FIG. 8, with no pipe casing present;

FIG. 9 b is a section along line B-B in FIG. 9 a;

FIG. 10 is a simplified plan view of the mechanism of FIGS. 14 showingthe rollers in their non-engaged position;

FIG. 11 shows the rollers after they have rolled into a partiallyengaged position;

FIG. 12 shows the rollers in their fully engaged position and deformingthe pipe string;

FIG. 13 a is a front view of a hand held socket wrench;

FIG. 13 b is a side view of the wrench of FIG. 13 a;

FIG. 13 c is a cross-section taken along line C-C in FIG. 13 a;

FIG. 14 is a cross-sectional side view of a slip-type elevator; and

FIG. 15 is a plan view of the elevator of FIG. 14.

Referring to FIG. 2, a gripping mechanism designated generally at 1comprises a pair of jaws 2,3 which are each mounted on respective pivotshafts 4,5. The jaws 2,3 can be pivoted apart by handles 6,7 to the openposition shown in FIG. 6, in which a pipe string 8 can be introducedinto the bore 39 between the jaws. The jaws are then closed and securedby means of a closing key 9.

Referring to FIG. 1, each jaw 2,3 carries a respective cage 10,11 (notshown in FIG. 2). The two cages are identical so only cage 10 will bedescribed in detail. The cage 10 has a semi-cylindrical body portion 14with upper and lower flanges 12,13. FIG. 4 a shows the cage 10 as viewedfrom inside the bore between the jaws with the pipe string 8 removed. Asshown in FIG. 4 a, the upper flange 12 carries a fastener 15 whichsecures a leaf spring 16 to the underside of the flange 12. The leafspring 16 has a pair of semicircular projections which each engage arelatively wide upper end of a respective roller 47 to apply a downwardbiasing force. The rollers 47 are frustoconical in shape and formed from420 stainless steel. The rollers 47 each protrude partially through arespective tapered slot 20,21 which is slightly narrower than therollers to prevent the rollers from passing through the slots. Therelatively narrow lower ends of the rollers are biased against the baseof the slots 20,21 by the leaf spring 16 to secure the rollers in place.

Referring to FIG. 1, the upper and lower flanges 12,13 each have guides22,23 which are received in respective upper and lower cage grooves inthe jaws 2,3. The upper cage groove 24 is shown in the plan view of FIG.2. The upper cage groove 24 contains a return spring 25 shown in FIG. 1which applies an upwards biasing force to the cage guide 22.

Each cage 10,11 can be driven downwards against the force of the returnspring 25 by a respective actuation mechanism. Only the actuationmechanism driving cage 11 will be described. The mechanism comprises anL-shaped actuation arm 30 pivotally mounted to the jaw 3 by a rose joint31. Referring to FIG. 3, a plate 32 fixed to the jaw 3 has an L-shapedslot 33 which receives the actuation arm 30. To drive the cage 11 downto its engaged position, the actuation arm 30 is lifted up from theposition shown in FIG. 1 (in which the arm engages the lower face 34 ofthe slot 33), then rotated until the arm 30 engages face 35 of slot 33.The arm 30 pushes down onto the cage to drive it to the lowered, engagedposition. For illustration, the cage 10 (and its associated actuationmechanism) is shown in its engaged position in FIG. 1 and the cage 11 isshown in its unengaged position.

As the roller 47 slides axially down to its engaged position, thecorrespondingly tapered inner cam surface 36 of the jaw 2 wedges theroller against the pipe string. This secures the pipe string againstrelative axial movement.

Preferably the internal angle of taper 37 of the cam surface 36 and theroller is greater than 0 degrees and less than 60 degrees. Morepreferably the internal angle of taper 37 is in the range of 3 to 5degrees. The angle of taper is exaggerated in the drawings for purposesof illustration.

The cam surface 36 is formed with a series of V-shaped recesses 38arranged around the circumference of the bore 39 which receive therollers, as shown in the plan view of FIG. 2. These recesses act to urgethe rollers against the pipe string as described below with reference toFIGS. 10-12. In the non-engaged position of FIG. 10 the rollers 47 areeach centered in their respective recesses 38 in the cam surface 36. Ifa torque is applied to the pipe string (or equivalently if the cages arerotated) the rollers will roll around the pipe string 8. As the rollersmove, they are urged by the cam surface towards the pipe string to theposition shown in FIG. 11 in which they engage the pipe string. As therollers continue to move, they are wedged into the pipe string and causethe pipe string to deform as shown in FIG. 12. Such deformation could bemeasured, for example, by a strain gauge attached to the inner or outercircumference of the pipe string.

However, the pipe string only needs to deform a small amount in order tofly grip the rollers. Therefore, the pipe casing 8 is not deformedbeyond its elastic deformation limit (either during initial gripping orwhen the pipe casing is being rotated) and when the rollers are releasedto the non-engaging position of FIG. 10, the pipe casing 8 relaxes backto its undeformed state.

It will be appreciated that the range of movement of the rollers 47, andthe degree of deformation of the pipe string 8, have both beenexaggerated in FIGS. 10-12 for purposes of illustration.

The actuation mechanism shown in FIGS. 1-3 drives the cages downwards toengage the rollers with the pipe string. An advantage of thisarrangement is that a wide variety of pipe string diameters can beaccommodated by varying the range of movement of the cages.

In an alternative arrangement illustrated in FIG. 4 b, the cages arerotated by alternative actuation mechanisms (not shown) to engage therollers with the pipe string. In this case, the leaf spring 16 isreplaced with upper leaf springs 40,41 and lower leaf springs 42,43. Theleaf springs 40-43 each have a respective base secured to a cage flange12/13 and a pair of arms which grip opposite sides of the roller. Whenthe cage is rotated, force is applied to the rollers by the spring arms,causing the rollers to roll round the pipe string.

In a further alternative arrangement, two different actuation mechanisms(not shown) are provided-one to drive the rollers downwards, and anotherto rotate the rollers. The roller mounting system for such a mechanismis shown in FIG. 4 c. Each fastener 15 secures leaf spring 16 to flange12. Each fastener 15 also secures a second leaf spring having a base andtwo arms 45,46 which each apply a sideways biasing force to a respectivedifferent roller.

Referring to FIGS. 5, 5 a and 6—the gripping mechanism 1 is mounted, inuse, in a tong 50. The mechanism 1 is housed between a pair of adapterplates 51. Pipe string 8 is introduced by opening gate 53 and jaws 2,3(see FIG. 6) and moving the pipe string 8 laterally into throat 52.

In use, an existing pipe string (not shown) is received in a boreholeand axially supported by a slip elevator (not shown). In order to attachan additional length of pipe string 8, the existing pipe string issecured against torque by a set of backup jaws (not shown) and theadditional length 8 is gripped by the tong 50 and screwed into theexisting pipe string. Large torques are required to ensure a gas tightseal between the coupled lengths of pipe string.

It will be appreciated that the mechanism of FIGS. 1-3 can be invertedas shown in FIG. 7. In this case the angle of taper of the rollers 47′and cam surface 36′ are reversed, and the cages are pulled upwards bytheir respective actuation mechanisms.

In a further alternative arrangement shown in FIGS. 8, 9 a and 9 b, therollers are ‘top-and-tailed’. Specifically, there are six downwardlydirected rollers 70 which alternate with six upwardly directed rollers71. Referring to FIGS. 9 a and 9 b: the downwardly directed rollers 70are mounted in a first cage 72 and the upwardly directed rollers 71 aremounted in a second cage 73. The cage 72 has a series of downwardlypointed fingers 74 and the cage 73 has a series of upwardly pointedfingers 75 which interlock with the fingers 74. Windows 76 are providedto allow relative axial movement between the two sets of fingers.

Each cage is driven up or down by a respective actuation mechanism (notshown), and is mounted in a respective cage groove 77,78 containing areturn spring 79,80, shown in FIG. 9 b.

The rollers 71 are urged against the pipe casing by a correspondinglytapered cam surface 81 with a V-shaped recess shown in FIG. 8, and therollers 70 are urged against the pipe casing by a similar cam surface(not shown).

An advantage of the arrangement of FIGS. 8-9 b is that the rollers canbe more densely packed than in the arrangement of FIG. 1.

Referring to FIGS. 13 a-13 c, a socket wrench designated generally at100 has a handle 101 and a head 102 having a bore defined by a camsurface 103 shown most clearly in FIG. 13 c. A cage mounted in the borecomprises a cylindrical body portion 106 with a pair of flanges 104,105.The body portion 106 has eight tapered windows which each receive arespective tapered roller 107.

A generally cylindrical socket member 108 is formed with a largehexagonal socket 109 on one side and a small hexagonal socket 110 on theother side. The member 108 has a series of holes arranged around itsperiphery each housing a coil spring and indent ball 111,112.

The rollers 107 can be engaged with the member 108 in two ways. In onealternative, by pushing the member 108 with the thumb in a directionindicated by arrow A (while holding the handle 101 still), the member108 moves the indent ball 111 which engages the cage flange 104. Thecage then engages the rollers 107 and slides them along cam surface 112.The cam surface 112 forces the rollers against the member 108 to lockthe member 108 in place. A nut can then be received in either of thesockets 109,110 and rotated by rotating the handle 101 in eitherdirection. The rollers can be disengaged by pushing the member 108 inthe opposite direction to arrow A with the thumb.

In a second alternative, the rollers can be engaged by rotating the cagewith an actuating handle 113. The handle 113 can be moved to the left orright (as viewed in FIG. 13 a). The cam surface 103 is formed withV-shaped recesses shown in FIG. 13 a which urge the rollers 107 againstthe member 108 when the cage is rotated.

A slip type elevator is shown in FIGS. 14 and 15. The elevator has agenerally cylindrical body portion 120 which is formed as a singlepiece, and is not split and hinged as in the tong mechanism shown inFIGS. 1-7. The body portion has a bore which receives a pipe string 121.The pipe string 121 is gripped by thirty rollers, arranged as threelayers of ten rollers. The upper layer of ten rollers 130 is shown inthe plan view of FIG. 15. Two rollers in each layer 130,131,132 areshown in the sectional view of FIG. 14.

The upper layer of rollers 130 is confined by a guide 122 shown in FIG.14 but omitted from FIG. 15 for clarity. Each layer of rollers issupported by a respective cage comprising a circular ring 123 and flange124 which is formed with a series of tapered slots (not shown) whichreceive the rollers. The three cages are each coupled to a handle 125.When the handle 125 is lifted up, the cages are lowered which allows therollers to drop due to gravity. As the rollers slide down they areforced by respective cam surfaces 126 against the pipe string 121. Theweight of the pipe string 121 can then be supported by the rollers. Theweight forces are transferred to the body portion 120 which is attachedto a rig floor (not shown) by three supports 127,128,129 shown in FIG.15. In an alternative arrangement (not shown) the weight forces may betransferred to bails by lugs.

If the pipe string 121 is rotated, the rollers roll up their V-shapedrecesses in the cam surface (shown in FIG. 15) and are forced againstthe pipe string, thus resisting the rotational movement.

The mechanism shown in FIGS. 1-13 (with a single row of rollers) is ableto transfer axial load and torque. However, the ability to transferaxial load is increased when torque is also present. Where the mechanismis employed in a slip elevator, then torque may not be present. This iswhy multiple rows of rollers are present in the embodiment of FIGS. 14,15: to provide increased ability to resist axial loads in the absence oftorque, whilst not deforming the pipe casing beyond its elasticdeformation limit. Although only three rows of rollers are shown in FIG.14, a larger number of rows (for instance fifteen) may be employed ifnecessary.

1. Gripping apparatus comprising a plurality of rollers which taperaxially from a relatively narrow end to a relatively wide end; and abody having a cam surface which is shaped so as to urge the rollersagainst a gripped member, when in use, when the rollers translateaxially with respect to the cam surface, and which is also shaped so asto urge the rollers against the gripped member when the rollers rollalong the cam surface.
 2. Apparatus according to claim 1 furthercomprising an actuator for generating relative movement between therollers and the cam surface to urge the rollers against the grippedmember.
 3. Apparatus according to claim 2 wherein the actuator isconfigured to generate relative axial movement between the rollers andthe cam surface.
 4. Apparatus according to claim 2 wherein the actuatoris configured to generate relative rolling movement between the rollersand the cam surface.
 5. Apparatus according to claim 2, wherein theactuator engages the rollers.
 6. Apparatus according to claim 5 whereinthe actuator comprises a plurality of resilient members, each coupledwith a respective roller.
 7. Apparatus according to claim 1 wherein theangle of taper of the rollers is approximately constant along the lengthof the rollers.
 8. Apparatus according to claim 1 wherein the rollersare substantially circular in cross-section.
 9. Apparatus according toclaim 7 wherein the rollers are substantially frustoconical. 10.Apparatus according to claim 1 wherein the direction of taper of therollers alternates between successive rollers.
 11. Apparatus accordingto claim 1 wherein the cam surface is formed with a plurality ofrecesses, each recess receiving a respective roller.
 12. Apparatusaccording to claim 1 wherein the body comprises two or more jaws whichcan be opened to admit the gripped member.
 13. Apparatus according toclaim 1, wherein the rollers are spaced axially with respect to eachother.
 14. Apparatus according to claim 13 wherein the rollers arearranged in two or more axially spaced rows.
 15. Apparatus for grippinga downhole tubular comprising gripping apparatus according to claim 1.16. Apparatus according to claim 15 wherein the apparatus is a powertong for gripping and rotating the downhole tubular.
 17. Apparatusaccording to claim 15 wherein the apparatus is a backup for gripping andsecuring the downhole tubular against rotational movement.
 18. Apparatusaccording to claim 15 wherein the apparatus is an elevator for securingthe downhole tubular against axial and rotational movement.
 19. A socketwrench comprising gripping apparatus according to any of claim
 1. 20. Amethod of handling a downhole tubular comprising gripping the tubularwith a plurality of gripping members in the form of tapered rollersarranged circumferentially around the pipe; and transferring rotationaland/or longitudinal forces to or from the tubular, wherein the tubularis gripped in such a manner so as not to exceed the elastic deformationlimit of the tubular while the forces are being transferred.
 21. Themethod of claim 20 further comprising the step of urging the grippingmembers against the tubular by a wedging action.
 22. The method of claim20, wherein the gripping apparatus is gripping apparatus according toclaim
 1. 23. The method of claim 20 further comprising the step ofcoupling the downhole tubular to an additional length of downholetubular.
 24. The method of claim 20 wherein the maximum deformation ofthe tubular lies in a range greater than 10% of the elastic limit of thetubular and less than 100% of the elastic limit of the tubular.
 25. Themethod of claim 20, comprising gripping the tubular with three or moregripping members.
 26. The method of claim 20, wherein the grippingmembers are metallic.